Hydrocarbon contamination of soil and groundwater at some locations is a well-known problem. Often the contamination results from past or ongoing industrial activity at the site or nearby. Subsurface contamination, particularly groundwater contamination, is a particularly serious problem because of the groundwater's ability to flow from a contaminated area to other nearby areas that were originally free of such contamination.
Some methods of treating contaminated groundwater are known in the art. Several of these methods employ microbial action in an attempt to bioremediate the contaminated groundwater. For example, U.S. Pat. No. 4,992,174 discloses a method for pumping contaminated groundwater to the surface microbiologically treating the water, and then recirculating the treated water to the contaminated site. Unfortunately, this method requires considerable above-ground equipment associated with the pumps and reactor. U.S. Pat. No. 5,486,291 teaches a microbial reactor that circulates contaminated groundwater through a bubbler supplied with air. The reactor contains fine particles used as microbe substrates. Unfortunately, air bubbles present in the reactor interfere with cell activity, see for example U.S. Pat. No. 4,649,114.
Additionally, U.S. Pat. No. 4,661,458 reveals that the fine particles collide during use resulting in damage to the organisms. Air bubbles present in the bioreactor also undesirably strip out volatile organic compounds present in the groundwater in the reactor.